Thermal conductivity cells are commonly used in the quantitative analysis of chemical constituents. A conductivity cell consists of a bridge network made up of thin resistive wires. The change in resistance of the bridge caused by the thermal conductivity of the material being measured provides an output signal which can be used to measure the amount of the material present in the gas stream flowing through the conductivity cell.
Great care must be exercised in the use and handling of a thermal conductivity cell to protect the thin filament wires. The cell is normally heated to a constant temperature for the thermal conductivity measurement. The heat is generated by passing current through the filament wires. It normally takes several hours before the resistors making up the bridge network in the thermal conductivity cell settle down or stabilize before the cell can be used. Also, when adjustments are made to the cell, such as the familiar offset adjustment, it takes several hours before the effect of the adjustment can be observed and several more hours if additional adjustments have to be made.
Also, it is important to minimize the effect of common mode or drift errors in the bridge and to reduce the effects of noise on the data signal representative of the amount of a constituent material in the sample being analyzed.